Wavelength-division-multiplexing (WDM) optical networks are becoming increasingly complex as the number of wavelength channels transportable over a single fiber increases and as the number of channels added/dropped at various sites within the network and/or exchanged between two or more optical networks increases. Increasingly, the costs associated with such complex networks are extremely high, in large part due to the need for many necessary monitoring and maintenance functions to be performed at the electrical signal layer rather than at the optical signal layer. Performance of a particular operation or maintenance function at the electrical layer is costly because it requires conversion of the optical signal conveyed over the network to an electrical signal before performing a particular function and then reconversion back to an optical signal for further transmission over the optical network.
For example, prior to the development of the optical amplifier, repeater sites incorporated within optical networks were implemented utilizing regenerators. A regenerator provided optical signal amplification by first converting an optical signal to an electrical signal, amplifying the electrical signal, and then reconverting the electrical signal to an optical signal for launching back onto the optical network. Thus, adjacent repeater sites were separated by optical transmission sections, with overhead being read and recreated at each repeater site. Network monitoring was only performed at portions of the network where such optical to electrical conversions were made, and therefore management of the network and network elements was performed entirely in the electrical layer. Such network management required additional data overhead as well, in order to transmit management and monitoring data within the network.
Development of the optical amplifier and wavelength-division-multiplexed networks have revolutionized the management of networks: repeaters are now incorporated within the optical layer; and so are wavelength multiplexers, optical Add/Drop sites, and optical crossconnects. An increasing percentage of the optical network has become transparent, bit rate independent, and format independent. These advances have enabled increased network bandwidth and speed. Unfortunately, monitoring and management of WDM network signal processes, such as fault detection, optical signal strength detection, and optical signal to noise ratio determinations, have not been incorporated as functions within the optical layer itself. That is, such network monitoring and management requires conversion of optical signals to electrical signals prior to performing the monitoring and/or management function, and then reconversion back to an optical signal for conveyance over the optical network.